1. Field of the Invention
The present invention relates to a communication apparatus using a switching unit, and more specifically to a bidirectional communication apparatus capable of controlling the quality of communication in bidirectional communications operations.
2. Description of the Related Art
With TV telephone communications, one subscriber transmits a picture and a voice to another subscriber, and vice versa. That is, bidirectional communication is performed.
FIG. 1 shows the configuration of the conventional bidirectional communications system.
A switching unit 12 at station A is connected to a switching unit 13 at station B via a communications line. They are connected to subscribers T.sub.11 -T.sub.1n and T.sub.21 -T.sub.2n respectively. For example, when subscriber T.sub.11 is connected to subscriber T.sub.21 at station B through TV telephone, a calling subscriber T.sub.11 requires high-quality communications through common TV telephone from calling subscriber T.sub.11 to called subscriber T.sub.21 and from called subscriber T.sub.21 to calling subscriber T.sub.11.
The above described switching units 12 and 13 at stations A and B are ATM switching units used in a broadband area ISDN, and connected to signal units 16 and 17 through control units 14 and 15 respectively. Signal units 16 and 17 transmit, for example, an outchannel signal according to system No. 7 common channel signaling and are connected through a signal line. As known in the art, ATM stands for asynchronous transfer mode, a standard for data communications using fixed length cells, each including a header field of routing information and an information field of data.
A picture and a voice signal outputted by subscriber T.sub.11 from a TV telephone is applied to a communications line through the switching unit 12 at station A. The signal transmitted through the communications line is applied to the TV telephone of each subscriber T.sub.21 through the switching unit 13 at station B. Then, the signal transmitted from subscriber T.sub.21 from a TV telephone is applied to the switching unit 12 at station A from the switching unit 13 through the communications path, and then outputted to subscriber T.sub.11. The signal transmission is performed through a TV communications line, and other control information is transmitted by the communications method No. 7. For example, a control signal from a terminal such as a TV telephone, etc. is applied by the control unit 14 to a signal line through the signal unit 16. Then, it is applied to the signal unit 17 through the signal line, and transmitted to the control unit 15. A control signal is transmitted to a called terminal in the reverse course. Thus, high quality communications can be performed and controlled through a communications line and a signal line as described above.
When bidirectional communications are performed through a TV telephone line, etc. as described above, uniform communication quality is normally required for both directions equally. However, in mail order systems, etc. using TV telephones, the communication quality of one way does not necessarily have to be the same as that of the other way. For example, a mail order company should send a high quality picture to a consumer when it delivers him a merchandise catalog. However, the consumer does not have to send back an order as a high quality picture. In this case, the communications fee will be reduced if the communication quality can be lowered to some extent for one way. Although the communication quality can be reasonably lowered for one way in the conventional method, high uniform quality communications are performed for both ways, thereby costing an unreasonably large amount.